GENES AND INHERIDENCE

What is an inheritance? To most people it is money or property that is left to them by family

or close friends. There is a more important kind of inheritance and that is genes. Every living thing has a set of characteristics inherited from its parent or parents. Scientists have done

extraordinary work with finding out about the genes we inherit from our parents.

The work really begun in 1822 when Gregor Mendel did experiments with pea plants. He basically laid the foundation of the science of genetics. I would like to start with a few "key" definitions before I explain what Mendel did.

1. Genotype - genetic makeup of an organism

2. Phenotype - physical characteristics of an organism

3. Allele - one of a number of different forms of a gene

4. Cross-over - process in which homologous chromosomes exchange portions of their chromatids during meiosis

5. Dominant - the one pair of alternative alleles that masks the effects of the other when both are present in the same cell or organism

6. Recessive - an allele that produces it characteristics phenotype only when its allele is identical

Gregor Mendel conducted an experiment with pea plants. He worked at a monastery in a garden. Like many plants or flowers, the pea plants use parts of their flowers to reproduce. The male part of each flower produces pollen, which contain the male sex cells. The female part of the flower produces eggs-female sex cells. When pollen fertilized an egg cell, a seed for a new plant is formed. Pea plants normally reproduce by self pollination, in which pollen fertilizes the egg cells in the very same flower. When Mendel started his experiment he had several different stocks of pea plants. They self pollinated and would produce offspring identical to themselves. One of his seed stock produced tall plants and another short plants. One stock had green seeds and the other yellow seeds.

Peas are known to cross - pollinate. With cross pollination male sex cells in pollen from the flower of one plant fertilize from cross pollination have two plants as parents.

Mendel selected pea plants that he could mate with each other. What he did was, he cut away the male part of a flower. Then he dusted that flower with pollen from a second flower. The resulting seed were crosses between the two plants!!!! Also, when he crossed these he noticed that all the offspring were green. Remember, he used the sex cells from green and yellow seed plants. He called the offspring F1. Then he allowed all of the green F1 plants to self-pollinate. He referred to these offspring as the F2 generation. Mendel noticed a 3:1 ratio in pod color. About 3/4 of the F2 plants had green pods and about 1/4 had yellow pods. This whole process was termed Mendel's

Law of Segregation. This law states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization.
From Mendel's law of segregation we see that the alleles for a trait separate when gametes are formed (through a type of cell division called meiosis). These allele pairs are randomly united at fertilization. If a pair of alleles for a trait are the same they are called homozygous. If they are different they are called heterozygous. In meiosis each plant has to inherit a single copy of every gene from both parents. Since each pea plant has two parents each plant must carry two complete sets of genes. Then when an organism produces its own gametes those two sets of genes must be separated from each other so that each gamete contains just one set of genes. Also, when the chromosomes are homologous they are referred to as diploid, which means two sets Chromosomes from each parent. If there are a single set of chromosomes and a single set of genes these are referred to as haploid, which means "one set." Meiosis has several steps it goes through to produce daughter cells. It is the process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. At the end of the steps meiosis produces four haploid daughter cells.

Genotype and phenotype play a key role. Genotype is the expression of genetic makeup and phenotype is the physical traits that you acquire. The genotype and phenotype are carried from generation to generation. The different forms of the genes are called alleles. This is where dominant and recessive come in. The dominance states that some alleles are dominant and others are recessive. An organism with a dominant allele for a particular form of a trait will always have that form. An organism with recessive allele for a particular form of a trait will have that form only when the dominant allele for the trait is not present. In Mendel's experiments,

the allele for tall plants was dominant and the allele for short plants was recessive. The allele for yellow seeds was dominant, while the allele for green seeds was recessive. To get a better understanding a Punnett Square, which was created by Reginald Punnett, the square that is for predicting the way alleles can combine. In this square the dominant and recessive are expressed with capital letters and lower case letters. If you see, for example TT, that would a dominant alleles and tt, would be recessive.

As part of this essay, we had to create a scenario of the Drosophilia fly ...........................
This picture shows the Punnett square and the offspring phenotype of the flies. Also, it show that the two fly's are heterogeneous. It also shows that one of the offspring inherited recessive genes.

Also, with this essay I did the dragon genetics lab. This was fun. It was like putting a puzzle together.
In this picture you can see that the dragons look identical. Also, you can see the chromosome X and the alleles that the dragon can inherited. It says at the bottom of the picture that I mastered the genotype to phenotype changes in the dragons. The genotype is the genetic makeup the dragon inherited and the phenotype is the physical traits, which you can see.

The research of genes and inheritance is very important. Scientists and researchers can predict what a child, for instance, may inherit. Some chromosomes fail to separate and the child my be born with downs syndrome. This particular disease is three copies of chromosome 21. We all inherit a set of chromosomes. Also, scientists can do a lot of testing on parents before they decide to get pregnant and see if a particular gene they have inherited could be expressed in the child's genes. Sometimes a particular disease may skip generation, but someone in that family is carrying "the gene" that will be expressed eventually. I should tell you that each cell in our bodies has 23 pairs of chromosome with a total of 46. There are 22 pairs of autosomes and one pair of sex chromosomes. The sex chromosomes are the X and Y and determine your gender.

I truly believe it is important for people to have genetic counseling before having a baby if they have certain family diseases that they are afraid of.